Non-visible areas of materials, such as the interiors of components, welds and composite materials can be analysed using ultrasonic testing. This type of non-destructive testing (NDT) utilises the reflection of sound waves to detect faults and features which would otherwise be very difficult to detect without destroying the component in the process. Ultrasonic testing is a common technique in the aerospace sector to test the integrity of materials at manufacture and during service.
Scanners tend to be of the portable type (i.e. more suited to in-service scanning) or non-portable type (specifically for production).
A feature of ultrasonic testing is that a couplant is required to aid transmission of the ultrasonic energy to the test specimen because the acoustic impedance mismatch between air and solids (i.e. such as the test specimen) is large. This causes reflection of the sound waves and a loss in scan quality if a couplant is not used. Couplants generally take the form of water or gel or a deformable solid.
Traditionally, ultrasonic testing has been limited in terms of inspection speed as the operation had to be carried out on a point-by-point basis. Improvements have led to the development of array scanning, or “paintbrush” scanning which permits a continuous scan over a surface to produce a two dimensional image of the desired region of the test component. Such equipment however is bulky and limited to use in a production (as opposed to service) environment and is not considered portable.
The issue of portability has been addressed with the development of the RapidScan system marketed by NDT Solutions Ltd. This system utilises a chassis to which a water filled rubber drum is rotatably mounted. An ultrasonic array is mounted to the axle and the water contained within the deformable rubber drum acts as the couplant.
The RapidScan system also features a rotary encoder mounted to the chassis proximate the drum. The chassis comprises a handle extending in the direction of travel of the RapidScan system.
In use, the chassis is held by the handle, proximate a workpiece with the drum and encoder contacting said workpiece, and moved such that the drum and encoder rotate. As this occurs, scanning takes place via the array. The scanned signal is fed from the array to a nearby computer for analysis. Simultaneously, the encoder transmits a signal to the computer such that the scanning position and hence the location of any features found can be determined.
There are various problems exhibited by this system. Firstly, the requirement for simultaneous contact of the drum and encoder means that the system cannot easily traverse significant changes in gradient of the workpiece. The device may become “grounded” (i.e. a part of the chassis between the encoder and drum may contact the workpiece). Alternatively, the drum or encoder may part contact with the surface leading to loss of useful results or loss of data relating to the distance travelled.
Also, the orientation of the chassis, and hence handle is fixed relative to the surface of the workpiece and hence the position of the user's hand is constrained in this respect. As such, in workpieces with particularly uneven surfaces, the user has to change the position of their hand relative to their arm/body several times. The various positions may also be uncomfortable to the user.
Also, it is often desirable to use a different frequency ultrasound array. Therefore it is necessary to carry several systems, each with different arrays to provide this functionality.
Further, the drum is mounted directly to the chassis. This limits the speed at which the array can traverse the workpiece as the user has to be careful not to allow the array to leave the workpiece surface at, for example, sharp changes in gradient of the surface or imperfections which the drum may “jump” over. If the drum leaves the workpiece the effect of the couplant is lost and the effectiveness of the scanner is significantly reduced.
Additionally, the stiff mounting arrangement between the drum and the chassis means that all of the force transmitted between the workpiece and the drum is transmitted to the user's hand, which may be uncomfortable in the case of shock or repetitive loading.
It is an aim of the present invention to overcome or at least mitigate at least one of the above problems.